Recently, mobile communication systems, such as WiMAX (World Interoperability for Microwave Access), LTE (Long Term Evolution), etc., which adopt OFDM (Orthogonal Frequency Division Multiplexing) modem scheme using a time-frequency conversion for baseband processing are known. Further, in the mobile communication systems which adopt the OFDM modem scheme using the time-frequency conversion for the baseband processing, a communication apparatus and a communication method are proposed to perform communication processing, such as a handover, at high speed and with high quality (see Patent Document 1: Japanese Laid-open Patent Publication No. 2008-270905, for example). Specifically, in the mobile wireless terminal disclosed in Patent Document 1, if it is determined in a power measuring part that a reception signal received by a communication part is smaller than or equal to a predetermined value, a frequency converting part performs calculations by enlarging a time-frequency conversion range for the received signal. The frequency converting part measures signal strength within the enlarged frequency range to detect a frequency in which the received signal has the signal strength greater than predetermined signal strength. The communication part performs a connection process using the signal of the detected frequency.
For example, in the case of the mobile communication system of LTE, a specification defines a maximum frequency bandwidth as 20 MHz, which is available for communications between mobile wireless terminals and base stations. If the mobile wireless terminal communicates with the base station using the maximum frequency bandwidth of 20 MHz, when the reception signal received by the communication part is smaller than or equal to the predetermined value, even the technique disclosed in Patent Document 1 cannot enlarge the time-frequency conversion range and thus cannot measure the reception signal strength in a band other than the band used for the communication.
Further, Patent Document 1 basically assumes a case where the mobile wireless terminal performs the handover during the communication, and thus does not specifically disclose how to search for the base station if the mobile wireless terminal is in a standby status or moved to dead space. Furthermore, in the case of the mobile wireless terminal which is applicable not only for the mobile communication systems adopting the OFDM modem scheme using the time-frequency conversion for the baseband processing but also for mobile communication systems (for example, WCDMA, CDMA 2000, GSM, etc.) adopting a modem scheme not using the time-frequency conversion for the baseband processing, Patent Document 1 fails to disclose how to search for the base station in the mobile communication systems which adopt a wireless accessing scheme which does not use the time-frequency conversion for the baseband processing.
The present invention was made in consideration of the matter described above, and it is an object of the present invention to provide a mobile wireless terminal, a method of measuring signal strength of a received signal, and a method of searching for a base station with which a time required to measure signal strength in a frequency band used may be shortened and power consumption involved in measuring the signal strength may be reduced.